The Nervous System

1. The Nervous System

2. Stimuli and Homeostasis • A stimulus is an internal or external change that brings about a response • Your nervous system helps your body adjust to changing stimuli • Homeostasis is the regulation of steady, life maintaining conditions within an organism, despite changes within its environment • Example: regulation of breathing and heartbeat

3. Nerve Cells • Neurons, or nerve cells, are the basic units of the nervous system • A neuron is made up of a cell body, branches called dendrites, and axons • Any message carried by a neuron is an impulse • Impulses move in only one direction • Dendrites receive impulses from other neurons and send them to the cell body • Axons carry impulses away from the cell body

5. Types of Nerve Cells • Sensory neurons receive information and send impulses to the brain or spinal cord • Interneurons send the impulses to motor neurons • Motor neurons send impulses from the brain or spinal cord to muscles throughout your body

6. How Impulses Move • Neurons do not touch each other • Neurons are separated from each other by a small space called a synapse • When an impulse reaches the end of an axon, the axon releases a chemical • The chemical flows across the synapse and stimulates an impulse in the dendrite of the next neuron

7. Divisions of the Nervous System • Two major divisions: the central nervous system and the peripheral nervous system • The central nervous system is made up of the brain and spinal cord • The brain is the control center for all activities in the body • Made up of billions of neurons • Spinal cord is made up of bundles of neurons

8. Peripheral Nervous System • All the nerves outside the CNS that connect the brain and spinal cord to other body parts are part of the peripheral nervous system • Peripheral nerves branch out from the spinal cord and connect to the rest of the body • Two major parts • The somatic system controls voluntary actions • The autonomic system controls involuntary actions

9. Reflexes • A reflex is an involuntary, automatic response to a stimulus • Allows the body to respond without having to think about what action to take • Reflexes are controlled in the spinal cord, not the brain

10. The Brain • Made up of three main parts • The cerebrum controls thoughts and voluntary actions • Receives the sensations produced by your senses • The cerebellum controls balance and coordination • The brain stem controls involuntary processes

11. Multiple Sclerosis • A disease that eats away at the protective covering of your neurons • Interferes with the communication between your brain and your body